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Houston Chronicle July 15, 2005

Shuttle could lift off Sunday, but odds slim

By Mark Carreau

CAPE CANAVERAL, FLA. - Still struggling to explain a problem with a faulty space shuttle fuel gauge, NASA said Thursday that Discovery could lift off no sooner than Sunday but did not rule out a postponement until September.

NASA mission management team chief Wayne Hale said the chances of a Sunday liftoff "are not high."

"I wish I had more answers," he said of the faulty reading from one of four sensors that caused the space agency to scrub Wednesday's scheduled launch of Discovery on the first shuttle mission since the 2003 Columbia accident.

"The repair that might get us to Sunday is if we go in and wiggle some of the wires and find a loose connection. But, I got to tell you," Hale said, "the folks that put those wires together and make the connections do a really good job."

The space agency has enlisted hundreds of engineers from field centers throughout the country to determine if the problem lies with the gauge itself, wiring inside the winged shuttle orbiter or what is emerging as the leading suspect — the aging transistors in an electronics box.

Standing by

Discovery was held at a 48-hour state of readiness, a posture managers intended to re-evaluate today. Astronauts Eileen Collins, Jim Kelly, Steve Robinson, Andy Thomas, Wendy Lawrence, Charles Camarda and Soichi Noguchi remained at the Florida shuttleport.

The difficulties underscore the dilemma faced by the space agency, which was widely criticized for safety lapses after the Columbia tragedy. NASA has vowed to fly safely but to retire the 24-year-old shuttle fleet by 2010 so it can replace the spacecraft with a ship capable of transporting explorers back to the moon.

"I don't think they're going to be interested in spending a huge amount of money on a novel maintenance (strategy). It would take a couple of years to get it implemented, and then they'd use it for only a few years," said John Pike, a space policy analyst with a Virginia-based national security think tank, globalsecurity.org.

"The challenge — the risk to the shuttle — is that they'll treat it as an old car they don't want to spend money on."

Aging shuttle, parts

At 21, Discovery is the oldest of NASA's three remaining shuttles and was last launched four years ago.

In April, a launchpad test revealed erratic readings from two of four fuel gauges embedded in the bottom of the external tank's hydrogen propellant container.

During a second test in May, the gauges worked, and managers credited new wiring and other circuitry. After the tank was later replaced to address other safety concerns, NASA decided not to repeat the test a third time.

Changes to Discovery included a piece of electronics called a "point sensor box" that is crucial to the fuel gauges that caused the postponement.

The point sensor box aboard Discovery was taken from Endeavour, at 13 the youngest orbiter in the shuttle fleet. Later, NASA managers learned the box contained 20-year-old transistors showing signs of degradation in non-space agency hardware.

Because the sensor box functioned in pre-installation tests, mission managers were confident it would work.

Now, shuttle managers are preparing a replacement in case their trouble-shooting of the fuel-gauge problem points to the box.

They said Thursday that an existing box that had been considered a replacement provides lower voltage than needed.

The assembly of another point sensor box will take 10 to 20 days, Hale said.

If Discovery does not lift off by July 31, the launch would be postponed until September.

The fuel gauges are designed to signal the shuttle's three rocket engines to shut off when the hydrogen propellant supply is nearly exhausted to lower the risk that the engines would churn without fuel and trigger an explosion.

Normally, the shuttle's flight-control computer signals the engines to turn off when the spacecraft reaches a velocity of about 5 miles per second. If a problem prevents the command from reaching the engines, the fuel gauges would order the shutdown.

The gauges become even more crucial if there is a fuel leak, Kinard said.

That happened aboard Columbia in 1999 with Collins in command. The shuttle, which reached orbit safely, leaked fuel through a hydrogen cooling line coiled inside the rocket nozzle.

As Columbia lifted off, a piece of debris perforated several of the lines, and the engines responded by increasing consumption of liquid oxygen. The oxygen fuel gauges triggered a safe shutoff before trouble developed.